The present invention relates generally to a method and apparatus for the installation of a cured in place liner within the interior of a conduit or pipeline, such as a sewer pipe, and, more particularly, to a method and apparatus for sealing the end of the liner and for securing a cable to the liner for installation.
It is generally well known that conduits or pipelines, particularly underground pipes, such as sanitary sewer pipes, storm sewer pipes, water lines and gas lines, that are employed for conducting fluids frequently require repair due to fluid leakage. The leakage may be inward, from the environment into the interior or conducting part of the pipe, or outward, from the conducting part of the pipe into the surrounding environment. Leakage of this type may be due to improper initial installation of the pipe, deterioration of the pipe itself due to normal aging or to the effects of conveying corrosive or abrasive materials, cracking of the pipe or of pipe joints due to environmental conditions such as earthquakes, the movement of large vehicles or similar natural or man made vibrations, or any other such causes. Regardless of the cause, such leakage is undesirable and may result in waste of the fluid being conveyed by the pipe, in damage to the surrounding environment and in the possible creation of dangerous public health hazards.
Because of ever increasing labor and machinery costs, it is becoming increasingly more difficult and less economical to dig up and replace underground pipes, or portions or sections of such underground pipes, that may be leaking. As a result, various methods have been devised for the in situ repair or rehabilitation of the existing pipes, thereby avoiding the expenses and hazards associated with digging up and replacing the pipes or pipe sections. One of the more successful pipe repair or rehabilitation processes that is currently used is called the Insituform.RTM. Process and is described in U.S. Pat. Nos. 4,009,063; 4,064,211; and 4,135,958, the contents of all of which are incorporated by reference herein.
Briefly, in the Insituform Process, an elongated flexible tubular liner of a felt fabric, foam or similar resin impregnable material that has been impregnated with a thermosetting synthetic catalyzed resin is installed within the existing pipe. The impregnated liner may be pulled into the conduit by a rope or cable, and a fluid impermeable inflation bladder or tube is then everted within the liner. Generally, however, the liner is installed utilizing an inverting (or everting) process, as described in the latter two patents.
The flexible tubular liners have a smooth layer of relatively flexible, substantially impermeable material coating the outside of the liner in its initial state, which impermeable layer ends up on the inside of the liner after the liner is inverted. As the flexible liner is installed in place within the pipe, the liner is pressurized from within, preferably utilizing a fluid such as water, forcing the liner radially outwardly to engage and conform to the interior surface of the pipe. The resin is then cured to form a relatively hard, tight fitting, rigid pipe lining that effectively seals any cracks and that repairs any pipe or pipe joint deterioration in order to prevent further leakage either into or out of the pipe. The cured resin liner also serves to strengthen the existing pipe walls so as to provide added structural support for the surrounding overburden.
All of these existing liner insertion methods, especially for the installation of a liner into a large diameter pipe, require positive control of the insertion and inversion of the liner throughout the entire inversion process.
The known methods for providing the pressure necessary to invert the liner within the pipe and to push it along the length of the pipe must also involve means for controlling the feed rate of the liner, i.e., the rate at which the liner is inverted and pushed into the pipe. Generally, in the Insituform Process, the resin-impregnated liner, which is typically stored in layers, is placed at a manhole adjacent the conduit to be lined, and the leading end of the liner is sealingly clamped to the proximal inside end of an eversion tube in order to create a fluid seal. The pressurized fluid, such as water, then forces the liner to invert into the conduit. Various means have been provided for controlling the rate at which the liner inverts and is fed into the conduit. The typical means within the Insituform Process for controlling the "feed rate" of the liner is by restraining the trailing end of the resin-impregnated liner as it is everted into the conduit using a cable or a hold-back rope. By restraining the trailing uneverted end of the liner, the liner does not evert too quickly, thereby ensuring that the pressure is maintained within the liner.
In addition to being restrained, the trailing end of the liner must also be sealed so that, when the tube is fully everted, the pressurized water or other fluid within the pipe is contained. At times, these pressures can be large. For example, the hold-back force needed during eversion of a 60-inch diameter liner tube with a 30-foot head of water is in excess of 20,000 pounds. When the tube is fully everted, the end of the liner must resist double that force.
Various means have been proposed to secure a holdback rope or cable to the trailing end of the liner for restraining the trailing end of the liner and for distributing the pulling stress over the entire width of the end of the liner. It has been proposed to seal the liner at the point of attachment of the hold-back cable in order to prevent water from escaping through the uneverted end of the liner and penetrating into the resin-wet material of the uneverted and everted portions of the liner ahead. One such cable end seal is shown in U.S. Pat. No. 4,776,370, the contents of which are incorporated herein by reference.
In the process described in U.S. Pat. No. 4,776,370, a short length of cured synthetic resin film, such as "Tuftane", is bonded directly to the outside of the flattened trailing end of the liner to seal the end of the liner. A series of holes is then formed through the flattened end of the liner. Special plates or straps also having holes are spaced out along both sides of the flattened end of the liner such that those holes align with the holes through the liner. Fastening elements such as nuts and bolts are placed through the holes of both the plates and the liner in order to secure the plates to the liner and seal the end of the liner. The hold-back cable is then attached, either directly or by way of an additional connector, to the plates for regulating the feed rate of the liner.
Another prior art way of securing a cable or rope to the trailing end of the liner for sealing the end of the liner and for distributing the pulling stress over the entire width of the flattened liner end is to use a series of holes as shown in FIG. 1. In this method a liner 2 having a trailing end 4 is flattened, and a series of holes 11 is formed through liner 2. Metal grommets may optionally be placed in holes 11 as reinforcement. A cable or rope 10 is then woven through holes 11 across liner end 4, and a number of rope handles 12 are looped around cable 10 at the region where cable 10 passes through liner end 4. Handles 12 are then tied to a hold-back cable for restraining trailing end 4 of liner 2 and for controlling the rate of eversion. In both of these conventional methods, the points at which the holes are formed through the liner and at which the handles emerge from the end of the liner must all be sealed in order to prevent water or fluid leakage. The assembly of such sealed ends is time consuming, difficult and expensive, and the seals are rarely totally effective.
Accordingly, it is desirable to provide a method and apparatus for forming attachment points or holes for the holdback cable, such that these holes are fully sealed and distribute the pulling forces effectively across the width of the felt or the resin-absorbent material and such that the resulting seals withstand the pressure built up when the liner is completely inverted.